1. Field of the Invention
The present invention relates to a supporting structure of hydrophones for a towed array sonar system, and more particularly to a supporting structure of hydrophones for reducing unnecessary vibrations transmitted to the hydrophone used to sense acoustic waves underwater, and thus reducing output noises, thereby improving the sensing performance of a towed array sonar system.
2. Description of the Related Art
A towed array sonar system (TASS) is widely used in military and nonmilitary fields for an underwater geological survey and sensing of targets moving underwater. FIG. 1 schematically illustrates the configuration and using condition of such a towed array sonar system. Referring to FIG. 1, a towed array acoustic module M, which is a construction consisting of several hundred sensor packages 3 aligned with one another in the form of a straight line while respectively carrying hydrophones (not shown) therein, is connected at one end thereof to a towing cable C extending from the stern of a towing vessel S. A tail rope T is connected to the other end of the towed array acoustic module M. This towed array acoustic module M is used underwater while being towed by the towing vessel S.
The towed array acoustic module M includes several hundred hydrophones uniformly spaced apart from one another and received in an elastic hose 6 filled with an insulating oil 5. Each hydrophone is fixedly mounted in an associated one of the sensor packages 3. These sensor packages 3 are connected to one another by support ropes (not shown), respectively. Thus, several hundred sensor packages 3 are carried in the interior of the elastic hose 6 while being uniformly spaced apart from one another. In order to firmly support each hydrophone by an associated one of the sensor packages 3, an open cell foam or closed cell foam (sponge) is conventionally used. In this case, the hydrophone is wrapped up in the open cell foam or closed cell foam, and the resultant structure is fitted in the sensor package 3 having a hollow structure.
In the towed array sonar system having the abovementioned arrangement, an acoustic wave reflected by the seabottom or a target moving underwater reaches the elastic hose 6, and is then coupled to and received by the hydrophones via the insulating oil 5. Each hydrophone converts the received acoustic wave into an electrical signal which is, in turn, outputted.
However, the hydrophones are configured to generate an electrical signal not only in response to an acoustic wave, but also in response to motions of those hydrophones. For this reason, when mechanical vibrations, which may be generated due to vibrations induced due to motions of the towing vessel S and motions of the towing cable C and tail rope T, are undesirably transmitted to a hydrophone, they are exhibited in the form of noises in the signal finally outputted from the hydrophone. In this case, there may be a degradation in the sensing performance of the sonar system. Practically, conventional towed array acoustic modules have such a problem. Although the hydrophones are connected to the towing cable C having a length of several hundred to several thousand meters in order to minimize the effect of radiation noises generated from the it towing vessel S, they are subjected to an accelerated motion due to unstable motions or vibrations of the towing vessel S, vibrations induced by motions of the towing cable C and the tail rope T, that is, vibrations resulting from swirling flows or strumming vibrations. As a result, noises are exhibited in output signals of the hydrophones, thereby degrading the sensing performance of the towed array sonar system.
As mentioned above, in the acoustic module M of the conventional towed array sonar system, each hydrophone is fitted in an associated one of the sensor packages 3 in a state of being wrapped up in an open cell foam or sponge. These sensor packages 3 are connected to one another by support ropes (not shown) while being uniformly spaced apart from one another. In this arrangement, unstable motions and vibrations of the towing vessel S, vibrations induced by motions of the towing cable C and tail rope T, that is, vibrations externally generated, are transmitted to the hydrophones via the open cell foam or sponge as they are, thereby resulting in motions of the hydrophones. As a result, the output signals of the hydrophones receiving these vibrations contain an increased fraction of noise. Such an increased fraction of noise in output signals resulting from the above mentioned two mechanisms causes a degradation in the sensing performance of the towed array sonar system.
Therefore, the present invention has been proposed in view of the above mentioned problems involved in conventional towed array sonar systems, and an object of the invention is to provide a towed array sonar system capable of suppressing hydrophones from vibrating due to external vibrations such as vibrations generated due to the running of a towing vessel used in association with the towed array sonar system or vibrations induced by motions of a towing cable connected between the towed array sonar system and the towing vessel, thereby allowing those hydrophones to have low-noise characteristics providing an improved sensing performance.
Another object of the present invention is to provide a support structure of hydrophones, which supports the hydrophones in a state of respectively being firmly held in sensor packages, using a mechanism capable of suppressing those hydrophones from vibrating due to external vibrations, thereby improving the sensing performance of a towed array sonar system to which the hydrophones are applied.
In order to accomplish these objects, the present invention provides in a towed array acoustic module for a towed array sonar system including a plurality of sensor packages aligned in an elastic hose filled with an insulating oil, the sensor packages being connected to one another and supported by support ropes while being spaced apart from one another, and a plurality of hydrophones carried in an associated one of the sensor packages, a hydrophone support structure comprising: at least one elastic member arranged in an associated one of the sensor packages and adapted to support an associated one of the hydrophones in the associated sensor package while attenuating vibrations transmitted to the associated sensor package.
The elastic member comprises an annular hydrophone fixing portion fixedly mounted to the associated hydrophone, an annular sensor package fixing portion fixedly mounted to the associated sensor package, and elastic support portions each connected between the hydrophone fixing portion and the sensor package fixing portion and adapted to attenuate vibrations.
The elastic support portions of the elastic member are symmetrically arranged together in a circumferential direction around the associated hydrophone.
The elastic member is configured to allow a structure comprising the elastic member, the associated hydrophone and the insulating oil to have a natural frequency not higher than a frequency band of acoustic waves to be received by the associated hydrophone.